Guarantor Financial Information (CONDENSED CONSOLIDATING BALANCE SHEET) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Apr. 01, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2016
Condensed Balance Sheet Statements, Captions [Line Items]
Depreciation, network and other	$ 1,023	$ 977
Current Assets
Cash and Cash Equivalents	4,378	2,550		$ 6,610	$ 2,942
Short-term Investments	4,008			2,354
Accounts and notes receivable, net	3,492		$ 3,808	3,711
Due from Affiliate, Current	0			0
Device and accessory inventory	622		979	1,003
Prepaid expenses and other current assets	895		846	575
Total current assets	13,395			14,253
Investments in Subsidiaries	0			0
Property, plant and equipment, net	20,538			19,925
Costs to acquire a customer contract	1,294		1,219
Due from Consolidated Affiliate	0			0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	6,586			6,586
FCC licenses and other	41,368			41,309
Definite-lived intangible assets, net	2,245			2,465
Other assets	1,023		964	921
Total assets	86,449			85,459
Current Liabilities
Accounts Payable, Current	3,143			3,409
Accrued expenses and other current liabilities	3,658		3,927	3,962
Current portion of long-term debt, financing and capital lease obligations	4,846			3,429
Due to Affiliate, Current	0			0
Total current liabilities	11,647			10,800
Long-term debt, financing and capital lease obligations	35,771			37,463
Deferred tax liabilities	7,704		7,660	7,294
Note due to consolidated affiliate	0			0
Other liabilities	3,382		$ 3,451	3,483
Due to affiliate	0			0
Total liabilities	58,504			59,040
Commitments and contingencies
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	27,945			26,419
Stockholders' Equity Attributable to Noncontrolling Interest	52			63
Total stockholders' equity	27,893			26,356
Liabilities and Equity	86,449			85,459
Due from Affiliate, Noncurrent	0			0
Depreciation, equipment rentals	1,136	854
Consolidation, Eliminations [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Depreciation, network and other	0	0
Current Assets
Cash and Cash Equivalents	0	0		0	0
Short-term Investments	0			0
Accounts and notes receivable, net	(717)			(347)
Due from Affiliate, Current	(424)			(424)
Device and accessory inventory	0			0
Prepaid expenses and other current assets	0			0
Total current assets	(1,141)			(771)
Investments in Subsidiaries	(46,662)			(45,136)
Property, plant and equipment, net	0			0
Costs to acquire a customer contract	0
Due from Consolidated Affiliate	(1,717)			(595)
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	0			0
FCC licenses and other	0			0
Definite-lived intangible assets, net	0			0
Other assets	0			0
Total assets	(84,951)			(82,380)
Current Liabilities
Accounts Payable, Current	0			0
Accrued expenses and other current liabilities	(717)			(347)
Current portion of long-term debt, financing and capital lease obligations	0			0
Due to Affiliate, Current	(424)			(424)
Total current liabilities	(1,141)			(771)
Long-term debt, financing and capital lease obligations	0			0
Deferred tax liabilities	0			0
Note due to consolidated affiliate	(35,431)			(35,878)
Other liabilities	0			0
Due to affiliate	(1,717)			(595)
Total liabilities	(38,289)			(37,244)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(46,662)			(45,136)
Stockholders' Equity Attributable to Noncontrolling Interest	0			0
Total stockholders' equity	(46,662)			(45,136)
Liabilities and Equity	(84,951)			(82,380)
Due from Affiliate, Noncurrent	(35,431)			(35,878)
Depreciation, equipment rentals	0	0
Parent Company [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Depreciation, network and other	0	0
Current Assets
Cash and Cash Equivalents	0	0		0	0
Short-term Investments	0			0
Accounts and notes receivable, net	236			99
Due from Affiliate, Current	0			0
Device and accessory inventory	0			0
Prepaid expenses and other current assets	3			5
Total current assets	239			104
Investments in Subsidiaries	27,885			26,351
Property, plant and equipment, net	0			0
Costs to acquire a customer contract	0
Due from Consolidated Affiliate	6			1
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	0			0
FCC licenses and other	0			0
Definite-lived intangible assets, net	0			0
Other assets	0			0
Total assets	39,994			38,343
Current Liabilities
Accounts Payable, Current	0			0
Accrued expenses and other current liabilities	237			100
Current portion of long-term debt, financing and capital lease obligations	0			0
Due to Affiliate, Current	0			0
Total current liabilities	237			100
Long-term debt, financing and capital lease obligations	11,864			11,887
Deferred tax liabilities	0			0
Note due to consolidated affiliate	0			0
Other liabilities	0			0
Due to affiliate	0			0
Total liabilities	12,101			11,987
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	27,893			26,356
Stockholders' Equity Attributable to Noncontrolling Interest	0			0
Total stockholders' equity	27,893			26,356
Liabilities and Equity	39,994			38,343
Due from Affiliate, Noncurrent	11,864			11,887
Depreciation, equipment rentals	0	0
Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Depreciation, network and other	0	0
Current Assets
Cash and Cash Equivalents	3,962	2,034		6,222	2,461
Short-term Investments	4,008			2,354
Accounts and notes receivable, net	481			248
Due from Affiliate, Current	424			424
Device and accessory inventory	0			0
Prepaid expenses and other current assets	12			9
Total current assets	8,887			9,257
Investments in Subsidiaries	18,777			18,785
Property, plant and equipment, net	0			0
Costs to acquire a customer contract	0
Due from Consolidated Affiliate	1,711			0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	0			0
FCC licenses and other	0			0
Definite-lived intangible assets, net	0			0
Other assets	198			185
Total assets	53,140			52,218
Current Liabilities
Accounts Payable, Current	0			0
Accrued expenses and other current liabilities	414			341
Current portion of long-term debt, financing and capital lease obligations	1,817			1,832
Due to Affiliate, Current	0			0
Total current liabilities	2,231			2,173
Long-term debt, financing and capital lease obligations	10,348			10,381
Deferred tax liabilities	0			0
Note due to consolidated affiliate	11,864			11,887
Other liabilities	812			831
Due to affiliate	0			595
Total liabilities	25,255			25,867
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	27,885			26,351
Stockholders' Equity Attributable to Noncontrolling Interest	0			0
Total stockholders' equity	27,885			26,351
Liabilities and Equity	53,140			52,218
Due from Affiliate, Noncurrent	23,567			23,991
Depreciation, equipment rentals	0	0
Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Depreciation, network and other	1,023	977
Other Additional Capital	1,500					$ 42
Current Assets
Cash and Cash Equivalents	416	516		388	$ 481
Short-term Investments	0			0
Accounts and notes receivable, net	3,492			3,711
Due from Affiliate, Current	0			0
Device and accessory inventory	622			1,003
Prepaid expenses and other current assets	880			561
Total current assets	5,410			5,663
Investments in Subsidiaries	0			0
Property, plant and equipment, net	20,538			19,925
Costs to acquire a customer contract	1,294
Due from Consolidated Affiliate	0			594
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	6,586			6,586
FCC licenses and other	41,368			41,309
Definite-lived intangible assets, net	2,245			2,465
Other assets	825			736
Total assets	78,266			77,278
Current Liabilities
Accounts Payable, Current	3,143			3,409
Accrued expenses and other current liabilities	3,724			3,868
Current portion of long-term debt, financing and capital lease obligations	3,029			1,597
Due to Affiliate, Current	424			424
Total current liabilities	10,320			9,298
Long-term debt, financing and capital lease obligations	13,559			15,195
Deferred tax liabilities	7,704			7,294
Note due to consolidated affiliate	23,567			23,991
Other liabilities	2,570			2,652
Due to affiliate	1,717			0
Total liabilities	59,437			58,430
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	18,829			18,848
Stockholders' Equity Attributable to Noncontrolling Interest	52			63
Total stockholders' equity	18,777			18,785
Liabilities and Equity	78,266			77,278
Due from Affiliate, Noncurrent	0			$ 0
Depreciation, equipment rentals	$ 1,136	$ 854